Process for preparing filamentary tow



United States Patent 3,283,054 PROCESS FOR PREPARING FEAMENTARY TOW Terence Francis McDonald, Waynesboro, Va., assignor to E. I. do Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed June 27, 1963, Ser. No. 290,921 4 Claims. (Cl. 264-344) This invention relates to a method for the heat treatment of filaments from segmented elastomers. More particularly, it relates to the :heat treatment of a bundle of talc-coated spandex filaments and the prevention of interfilament adhesion within the bundle.

It is old in the art to Wet spin bundles of filaments of segmented elastomers. Immediately upon extrusion, the filaments are quite tacky; and if it is desired to pro-' duce a bundle of coalesced filaments, it is a relatively simple matter to bring the individual filaments together for purpose of coalescence. If, on the other hand, a tow or bundle of separate, continuous filaments is desired, care must be taken to prevent the filaments from sticking together. In the past, a particulate solid material, for example, talc, has been dispersed in'the coagulation both to prevent interfilament adhesion during spinning and extraction of residual solvent from the tow of elastic filaments. As taught in US. Patent 3,047,909, a heat treatment for improving the physical properties of the wet-spun filaments is firequently desirable. A level of talc on the filaments sufficient to prevent adhesion during the spinning operation and suflicient for subsequent textile processing is usually insufii-cient to prevent interfilament adhesion during the heat treatment. Conversely, a level of talc sufficient for protection during the heat treatment is excessive and often troublesome for textile processing of the heat-treated product.

It is an object of this invention to provide a process for heat-treating a bundle of spandex filaments while maintaining acceptable filament separation. It is a further object of this invention to provide a method for heatt-reating a talc-finished bundle of spandex, wherein the final bundle contains a not excessive amount of tale for subsequent processing.

These and other objects are accomplished by a process for heat treating a bundle of spandex filaments which comprises (1) heating a plurality of dry spandex filaments containing at least talc by weight at a temperature of at least 130 C. for at least five minutes, (2) washing the non-adhered talc particles from the filaments, (3) adjusting the tale content of the Washed filaments to at least 10% by weight, and (4) drying the filaments at a temperature below 130 C.

The segmented elastomer which makes up the spandex filament bundle is a copolymer consisting of segments of a high-melting, crystalline polymer alternating with segments of a low-melting, amorphous polymer. The crystalline, high-melting segment may be derived from, for example, a polyurea, polyurethane, polyamide, bis-ureylene polymer, or polyester. Tlhe low-melting, amorphous segment may be derived from, for example, a polyester, a polyether, or a hydrocarbon polymer.

The segmented copolymers described in several patents are useful in the practice of this invention. Among these are US. Patent 2,929,801, 2,929,802, 2,909,803, 2,929,804, 2,957,852, 2,962,470, 3,009,901, 3,040,003, 3,044,987, and 3,044,989. As disclosed in these references such segmented vcopolymers when in filament for-m display elongations at the break in excess of 200%. Although these segmented elastomers are described as substantially linear, it is not intended that segmented copolymers which have some branches extending from the polymer chain be excluded.

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In the conventional spandex wet spinning process, the filaments are spun from a solution of spandex polymer in a solvent, such as dimethy-lformamide. The solution is extruded into a coagulation bath containing particles of talc or some other solid in suspension to prevent interfilament adhesion. From the coagulation bath, the filament bundle is passed to an extraction bath in which a countercurrent flow of solvent-miscible liquid, such as water, usually containing no added talc, extracts the residual solvent. At this point, the filaments generally contain less than 2% by weight of solvent. For the practice of this invention, if less than 25% talc by weight remains on the filaments after passage through the extraction bath, a talc-slurry finish is applied so that the filaments will contain at least 25% talc by weight.

The tale finish may be applied to the filaments by passing the tow through a bath containing a 25% slurry of talc in water. Uniform penetration of the finish into the tow, essential in order to avoid webby streaks in the final product, is obtained by advancing the tow into the finish bath in the form of a wide, fiat, uniform ribbon. This configuration may be achieved by use of properly aligned, concave, driven rolls in the finish bath.

The talc content of the emerging tow is regulated by stripping off excess finish. This is conveniently accomplished by passing the tow between stripping pins at the exit of the finish bath. Preferably, the talc content is adjusted within the range of 35% to 45% by weight. The filaments are then dried to free them of residual water.

The dried, talc-coated bundle of spandex filaments is then heat-treated at a temperature of at least C. for a period of at least five minutes. The drying step may be combined, if desired, with the step of heat-treating. Since heat-treating temperatures below 130 C. require too long a time for a practical process, 130 C. or higher should be used in the practice of this invention. Preferably, the maximum temperature is C. although, in some cases, higher temperatures may be used if the particular spandex is not degraded thereby. At the temperature specified, it is necessary that a minimum of 25 talc by weight be present on the filaments to maintain adequate interfilament separation.

The heat may be supplied in any suitable form, such as hot gas or liquid, infrared radiation, ultrasonic energy, dielectric heating, or other, so long as it is controllable and can be used to maintain the temperature in the desired range. If an oven is used, it is sometimes advantageous to heat under an inert gas in order to prevent oxidative damage to the fibers. If a bath is used, a bath liquid must be chosen which will not cause sticking of the fibers and which is easily removed in the next step of this process. The heating is preferably carried out on a spandex tow which is under substantially restraint-free conditions.

By the procedure described above, approximately 3-4% by weight of talc is rather firmly bonded to the surface of the spandex fibers. Apparently, the solid particles of talc are fused to the plastic polymer surface during the heatsetting step.

After the heat treatment, the excess talc is removed by passing the tow rapidly through a hot-water bath under conditions of low stretch. The tension on the tow. is sufficient only to advance the threadline through the bath. The bath may be maintained at temperatures ranging from 20 C. to 100 C. but is preferably held at 90 C. This treatment not only removes excess talc'from the filaments but also by the combination of heat and drag separates the filaments within the bundle which may be bound together.

It has been found that at least 10% by weight of talc is required for textile processing of spandex tow and staple filament blends prepared therefrom. Therefore, if the spandex tow contains less than by weight of talc after the washing step, sufiicient additional 'talc is applied by use of the talc-slurry finish to bring the tale content to at least this level. If desired, the level of talc may be adjusted by passing the treated tow through squeeze rolls. The tow is finally dried at a temperature of less than 130 C. Any suitable method of heating, as described above, may be used for carrying out the drying step.

The continuous-filament tow produced by the process of this invention may be cut into staple. The elastic filaments of staple length may be blended with inelastic staple as taught in US. Patent 3,007,227, which blends are useful in the formation of elastic yarn. Staple blends may also be formed by proper blending of the continuous filament tow with a tow of inelastic continuous filaments and then cutting the blend of tows to staple length, as taught in US. Patent 3,077,006. The staple blends are useful for making a wide variety of elastic or stretchy products including woven, knitted and non-woven fabrics for use in universal fitting apparel, form-fitting upholstery, surgical stockings, and splint tapes.

The invention will be further illustrated, but is not intended to be limited by, the following examples in which parts and percentages are by Weight unless otherwise specified.

Example I A 6000-denier spandex tow is wet-spun as described in Example 1(a) of U.S. Patent 3,077,006. As described in said patent, the tow is washed in a hot water bath until the filaments contain less than ,0.5% dimethylformamide. The spandex tow is then passed through a talc slurry containing by weight of talcdispersed in 50% aqueous acetone. The tow is guided through the slurry by means of free-turning spreader rolls so that the talc is uniformly distributed on the tow. The tow is dried at 104 C. for three hours and is then heat-treated for one hour at 140 C. to improve the physical properties. LThus produced, the tow has a total denier of approximately 6000, denier per filament of 6, contains less than 2% moisture, and is Well coated wtih talc. The tow contains about 40% talc by Weight and can be blended with tows of inelastic fibers to make staple blends having entirely satisfactory properties except for the fact that processing on textile equipment is accompanied by a severe and troublesome dusting problem.

The heat-treated tow containing 40% talc is passed under low tension through a water bath approximately two feet in length and held at a temperature of about 90 C. The level of the talc on the dried tow is thereby reduced to about 8l0%. A tale finish is reapplied by passing the tow through the talc slurry described above. The amount of talc taken up from the slurry is regulated by passing the tow over wiper bars and between squeeze rolls, so that on emergence the tow contains approximately 15% talc and 70% water on a dry-weight basis. The tow is heated at about 100 C. until dry. It causes no dusting problem yet processes as well on textile equipment as the tow described in the preceding example.

Another sample of the spandex tow coated with talc (as described in the first paragraph of this example) is dried and heat-treated at 171 C. for fifteen minutes. Similar results after washing with water, reapplication of talc, and drying are obtained as with the sample described in the preceding paragraph.

Example II Spandex tow is made as described in Example I except that a talc slurry containing 10% talc in 50% aqueous acetone is applied initially to the wet-spun product so that the dried tow contains approximately talc by weight.

The tow is dried andtreated for fifteen minutes at 171 C. A large degree of interfilament adhesion is observed,

and the tow is unsatisfactory. for textile processing. The tow is passed through a water bath at 90 C. as described in Example I. No reduction in interfilament adhesion is observed.

Another sample of the spandex tow containing 20% talc is dried at 104 C. for three hours and heat-treated at 140 C. for one hour. The interfilament adhesion, though not as severe as with the tow described in the preceding paragraph, is too great for acceptable textile processing, The tow is passed through a water bath at 90 C. as described in Example I. No reduction in interfilament adhesion is observed.

Example III Spandex tow is made as described in Example I except that a tale slurry containing 10% talc in 50% aqueous acetone is applied initially to the Wet-spun product so that the dried tow contains approximately 25% talc by weight. After being dried and heat-treated as in Example ]T, the interfilament adhesion is too great for acceptable textile processing. After this product is passed through a water bath held at a temperature of -50 C., the interfilament adhesion is reduced to a barely acceptaw ble level. raised to 90 C., the interfilament adhesion is reduced still further-and is entirely acceptable.

As shown in the examples, the filaments in a spandex tow do not adhere to one another when the level of talc on the tow is sufliciently high; In such case, the washing with water merely removes excess talc. If the level of, talc is borderline, i.e., about 25%, a slight amount of interfilament adhesion occurs. Passage through the water bath then not only removes excess talc but also separates the stuck filaments. In such cases, hot water is most effective. If the level of talc on a spandex tow is too low, i.e., below 25 severe interfilament adhesion on heat treatment takes place, and the washing operation is ineffective regardless of the water temperature.

I claim:

1. A process for preparing a spandex tow which is substantially free from interfilament adhesion comprising the steps of (1) heating a spandex tow comprised of a plurality of filaments containing at least 25% by weight of talc at a temperature of at least C. for at least five minutes,

(2) washing said heat-treated tow to remove substantially all loose talc particles,

(3) adjusting the talc content of said filaments to provide at least 10% by weight of talc on said filaments, and thereafter (4i3ggyil-g said filaments 'at a temperature below 2. The process of claim 1 wherein the tale content of said filaments is adjusted before said heating within the range of 35% to 45% by weight before drying.

3. The process of claim 2 wherein said heating is carried out at a temperature between 130 C. and C.

4. The process of claim 3 wherein said heat-treated tow is washed in an aqueous bath at a temperature from 20 C. to 100 C.

References Cited by the Examiner ALEXANDER H. BRODMERKE-L, Primary Examiner. B. SNYDER, Assistant Examiner.

When the temperature of the water bath is 

1. A PROCESS FOR PREPARING A SPANDEX TOW WHICH IS SUBSTANTIALLY FREE FROM INTERFILAMENT ADHESION COMPRISING THE STEPS OF (1) HEATING A SPANDEX TOW COMPRISED OF A PLURALITY OF FILAMENTS CONTAINING AT LEAST 25% BY WEIGHT OF TALC AT A TEMPERATURE OF AT LEAST 130*C. FOR A LEAST FIVE MINUTES, (2) WASING SAID HEAT-TREATED TOW TO REMOVE SUBSTANTIALLY ALL LOOSE TALC PARTICLES, (3) ADJUSTING THE TALC CONTENT OF SAID FILAMENTS TO PROVIDE AT LEAST 10% BY WEIGHT OF TALC ON SAID FILAMENTS, AND THEREAFTER (4) DRYING SAID FILAMENTS AT A TEMPERATURE BELOW 130*C. 